1. Department of Applied Physics, Osaka University, Suita, Osaka 565-0871
2. Department of Physics, Osaka University, Toyonaka, Osaka 560-0043
3. Center for the Promotion of Research on Nanoscience and Nanotechnology, Osaka University, Toyonaka, Osaka 560-8531
4. Physics Department, De La Salle University, Taft Ave., 1004 Manila, The Philippines
5. Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8587